This invention relates to multiple blade, controllable pitch propellers of the class having two crankpins on each blade turning flange, and more particularly to means for achieving equal loading on the crankpins and crankpin linkages.
In controllable pitch propellers having two crankpins on each blade turning flange, the problem of equally loading the crankpins has always existed. The equal loading problem arises because the manufacturing accuracy necessary to make the various linkages equal in length (an absolute requirement in obtaining equal crank loading in such mechanisms) has heretofore been impossible to obtain. Prior attempts to achieve equal loading by the fitting and scraping of parts in the controllable pitch propeller have not been successful in obtaining linkages of the necessary equal length to provide equal crankpin and linkage loading. When the crankpin linkages in existing controllable pitch propeller assemblies are connected to the actuating mechanism (normally a hydraulic piston and cylinder) and tightened, some of the connections become tight while others are slack. Any attempt to fully tighten all the connections will overstrain some of the crankpin linkages while the remainder are merely snug. The parts that are overstressed during assembly will experience much higher loading during operation. Manufacturing inaccuracies in existing mechanisms result in placing most or all of th load onto one crankpin and its associated linkage, causing the mechanism to bind and become unworkable.
In my previous U.S. Pat. No. 3,676,016, I disclose a controllable pitch propeller having a double crank blade turning mechanism including a pivotable piston with self aligning connections to one set of crankpins to provide equal loading on all the crankpins. The structure described in my previous patent provides perfect, equal loading on the crankpins but comprises many parts, including a self-aligning connection to the actuating piston and, for propellers with four or more blades, including a secondary piston plate.
The principal object of this invention is to provide a controllable pitch propeller having a simplified, double crank blade turning mechanism with a single adjustment member in the connection between the actuating piston and one set of crankpins for taking up and compensating for the slack resulting from inherent manufacturing inaccuracies and to thus provide equal loading on all the crankpins.
Another object is to provide a double crank, blade turning mechanism having an adjustment member that automatically takes up slack in the mechanism when adjusted, that compensates for machining inaccuracies, is simple to install, and that provides equal loading on all crankpins.
Another object is to provide a single adjustment member to replace the plurality of shims and spacers used in conventional controllable pitch propellers, and the spherical washers and secondary piston plate disclosed in my previous patent.
Another object is to provide an adjustment member that is simply and easily adjusted to compensate for wear of the mechanism.
Other objects are to provide a mechanism that can be utilized on controllable pitch propellers having any number of blades and to provide a blade turning mechanism that has fewer parts than known controllable pitch propellers, that is of practical and durable construction, and that is simple and inexpensive to manufacture.
Still another object of the present invention is to provide a piston that can inherently compensate for unequal length crankpin linkages without the need for adjustment members and without overstressing the piston.